http://puu.sh/aNrOz/6b5d74dd41.jpg I've tried putting Yellorium ingots into the reactor by hand, pipe, AE2, and hopper, and am unable to. I also tried removing the coolant ports and was still unable to fuel it. This is a clean SP world, spawned used creative to get the blocks needed for the reactor and placed them, the reactor size/design was copied from a reactor I've used in 1.6.4. MC 1.7.10, Forge 1200, Modlist: http://pastebin.com/yBzPnj28

Thanks for the report, I'll look into this. It's probably a product of my big refactoring in X2.